New X-ray Clusters in the EMSS I: Modifications to the XLF

Abstract

The complete ensemble of Einstein Imaging Proportional Counter (IPC) X-ray images has been re-processed and re-analyzed using a multi-aperture source detection algorithm. A catalog of 772 new source candidates detected within the central regions of the 1435 IPC fields comprising the Extended Medium Sensitivity Survey (EMSS) has been compiled. By comparison, 478 EMSS sources fall within the same area of sky. A randomly-selected subsample of 133 fields was first examined. We found that most of these sources are either the summation of two or more lower count rate point sources that fall within the larger detection apertures or are single point sources, while \leq 2.3% of the full catalog of sources are extrapolated to be actual distant (z > 0.14) clusters whose extended X-ray structure kept them from being detected in the EMSS despite having sufficient total flux. We then constructed other subsamples specifically selected to contain those X-ray sources most likely to be clusters. Both a database search and an optical imaging campaign have found several new distant clusters, setting a firm lower limit on the number of new clusters in the entire catalog. We estimate that the original EMSS cluster sample is 72-83% complete. We update the Henry et al. 1992 EMSS distant cluster sample with more recent information, and use the redshifts and X-ray luminosities for these new EMSS clusters to compute a revised X-ray Luminosity Function (XLF). The addition of these new high-z, high-L_X clusters to the EMSS is sufficient to remove the requirement for ``negative'' evolution at high-L_X out to z~0.5. We conclude that the EMSS has systematically missed clusters of low surface brightness.

Accepted to ApJ, 32 pages, 8 figures, uses emulateapj5.sty, for associated data table see http://casa.colorado.edu/~lewisad/research/nemsscatalog.html

References in corpus (4)

• Distant Cluster Hunting I: A Comparison Between the Optical and X-ray Luminosity Functions from an Optical/X-ray Survey
• Cluster Evolution in the ROSAT North Ecliptic Pole Survey
• A Study of 3CR Radio Galaxies from z = 0.15 to 0.65. I. Evidence for an Evolutionary Relationship Between Quasars and Radio Galaxies
• New X-ray Clusters in the EMSS II: Optical Properties

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• Distant Cluster Hunting II: A comparison of X-ray and optical cluster detection techniques and catalogs from the ROX Survey
• Evidence for Cluster Evolution from an Improved Measurement of the Velocity Dispersion and Morphological Fraction of Cluster 1324+3011 at z = 0.76
• Evolution of the Cluster X-ray Luminosity Function
• Batch discovery of nine z~1 clusters using x-ray and K or R,z' images
• The Evolution of Radio Galaxies and X-ray Point Sources in Coma Cluster Progenitors Since z~1.2
• A Deep Chandra Observation of the Distant Galaxy Cluster MS1137.5+6625
• New X-ray Clusters in the EMSS II: Optical Properties